238 THE RESPIRATORY APPARATUS 



of the thyroid cartilage, reaching upward as high as 

 the upper border of that cartilage, and its mucous 

 membrane presents the orifices of sixty or seventy 

 glands. This space has a fibrous capsule. 



The muscles of the larynx are divided into extrinsic 

 and intrinsic the former will be found under the 

 muscle system. The latter are: 



Crico thyroid. Posterior crico-arytenoid. 



Thyro-arytenoid. Lateral crico-arytenoid. 

 Thyro-epiglotticus. Arytenoid (single). 



Actions of the intrinsic muscles: (1) Those which 

 open and close the glottis. (2) Those which regulate 

 the degree of tension of the vocal cords. 



1. The two posterior crico-arytenoids open the 

 glottis; and the arytenoid and the two lateral crico- 

 arytenoids close it. 



2. The two cricothyroids regulate the tension of 

 the vocal cords, and elongate them by the same action; 

 the two thyro-arytenoids relax and shorten them. 



Phonation, Articulate Speech. Phonation is the 

 phenomenon whereby the animal and human being 

 are enabled to utter vocal sounds, due to the vibration 

 of two elastic membranes, the vocal cords, which 

 cross the opening of the larynx from before backward, 

 and which are thrown into vibration by the air forced 

 from the lungs. 



Articulate speech is a modification of the vocal 

 sounds or the voice produced by the teeth and the 

 muscles of the lips and tongue, and is employed for 

 the expression of ideas (Brubaker). 



The Trachea. The trachea is a membranocar- 

 tilaginous tube, flattened behind, continuous above 

 with the larynx, and below dividing into the two 

 bronchi. 



The trachea consists of sixteen to twenty incomplete 

 cartilaginous rings connected by a fibrous membrane. 



